1. Field of the Invention
The invention relates to a transmission control system for an automatic transmission.
2. Description of the Prior Art
Recently, in many of automatic transmissions for a vehicle, the shift pattern can be changed. For example, an economy mode shift pattern and a power mode shift pattern in which shift lines are shifted toward the high vehicle speed side as compared with the economy mode shift pattern are prepared, and one of the shift patterns can be manually selected.
Further there has been proposed an automatic transmission in which one of a plurality of shift patterns is automatically selected on the basis of the engine load. For example, in the automatic transmission disclosed in Japanese Patent Publication No. 57(1982)-8983, the automatic transmission normally shifts according to an economy mode shift pattern, and when the engine load exceeds a predetermined reference value, e.g., the value corresponding to the throttle opening of 3/4, the automatic transmission shifts according to a power mode shift pattern. That is, it is considered that the engine load is heavier than the reference value means a large engine output power requirement, and the power mode shift pattern is automatically selected.
In the automatic transmission disclosed in Japanese Patent Publication No. 51(1976)-22698, the shift pattern is changed to the power mode shift pattern when the accelerator pedal is abruptly pushed down, that is, when the rate of change of the engine load exceeds a predetermined reference value.
However, in the automatic transmissions disclosed in the patent publications described above, an optimal shift pattern cannot be always selected since the reference values are fixed.
That is, in the case of the automatic transmission disclosed in Japanese Patent Publication No. 57(1982)-8983, when the vehicle cruises at a constant speed under engine load slightly heavier than the reference value, the power mode shift pattern will be selected though the economy mode shift pattern is preferred in view of fuel economy. On the other hand, when the accelerator pedal is pushed down with intention of accelerating the vehicle while the vehicle is cruising at a constant speed under engine load which is substantially lighter than the reference value, the shift pattern is kept the economy mode shift pattern until the engine load exceeds the reference value and accordingly, the vehicle cannot be sufficiently accelerated.
In the case of the automatic transmission disclosed in Japanese Patent Publication No. 51(1976)-22698, proper acceleration for the load on the vehicle, the inclination of the road, or the like cannot be obtained since the shift pattern is switched solely depending upon the rate of depression of the accelerator pedal. For example, the driver is apt to largely push down the accelerator pedal before an ascending slope without intention of accelerating the vehicle, and in such a case, the shift pattern is switched to the power mode shift pattern against his will.